Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Loading...
Galera Management in MariaDB handles synchronous multi-master replication, ensuring high availability, data consistency, failover, and seamless node provisioning across clusters.
The most recent release of is: Stable (GA) Download Now, Alternate download from mariadb.org
The current versions of the Galera wsrep provider library are 26.4.21 for Galera 4. For convenience, packages containing these libraries are included in the MariaDB .
Currently, MariaDB Galera Cluster only supports the storage engine (although there is experimental support for and, from , ).
MariaDB Galera Cluster is powered by:
MariaDB Server.
The patch for MySQL Server and MariaDB Server. The patch currently supports only Unix-like operating systems.
The .
The patch has been merged into MariaDB Server. This means that the functionality of MariaDB Galera Cluster can be obtained by installing the standard MariaDB Server packages and the package. The following version corresponds to each MariaDB Server version:
MariaDB Galera Cluster uses 4. This means that the patch is version 26 and the is version 4.
See for more information about how to interpret these version numbers.
See for more information about which specific version is included in each release of MariaDB Server.
In supported builds, Galera Cluster functionality can be enabled by setting some configuration options that are mentioned below. Galera Cluster functionality is not enabled in a standard MariaDB Server installation unless explicitly enabled with these configuration options.
During normal operation, a MariaDB Galera node consumes no more memory than a regular MariaDB server. Additional memory is consumed for the certification index and uncommitted write sets, but normally, this should not be noticeable in a typical application. There is one exception, though:
When a node is receiving a state transfer, it cannot process and apply incoming writesets because it has no state to apply them to yet. Depending on a state transfer mechanism (e.g.) the node that sends the state transfer may not be able to apply writesets as well. Thus, they need to cache those writesets for a catch-up phase. Currently the writesets are cached in memory and, if the system runs out of memory either the state transfer will fail or the cluster will block waiting for the state transfer to end.
To control memory usage for writeset caching, check the : gcs.recv_q_hard_limit, gcs.recv_q_soft_limit, and gcs.max_throttle.
Before using MariaDB Galera Cluster, we would recommend reading through the , so you can be sure that it is appropriate for your application.
To use MariaDB Galera Cluster, there are two primary packages that you need to install:
A MariaDB Server version that supports Galera Cluster.
The Galera wsrep provider library.
As mentioned in the previous section, Galera Cluster support is actually included in the standard MariaDB Server packages. That means that installing MariaDB Galera Cluster package is the same as installing standard MariaDB Server package in those versions. However, you will also have to install an additional package to obtain the Galera wsrep provider library.
Some methods may also require additional packages to be installed. The SST method is generally the best option for large clusters that expect a lot of loads.
MariaDB Galera Cluster can be installed via a package manager on Linux. In order to do so, your system needs to be configured to install from one of the MariaDB repositories.
You can configure your package manager to install it from MariaDB Corporation's MariaDB Package Repository by using the .
You can also configure your package manager to install it from MariaDB Foundation's MariaDB Repository by using the .
On RHEL, CentOS, Fedora, and other similar Linux distributions, it is highly recommended to install the relevant from MariaDB's
repository using or . Starting with RHEL 8 and Fedora 22, yum has been replaced by dnf, which is the next major version of yum. However, yum commands still work on many systems that use dnf.
To install MariaDB Galera Cluster with yum or dnf, follow the instructions at .
On Debian, Ubuntu, and other similar Linux distributions, it is highly recommended to install the relevant from MariaDB's repository using .
To install MariaDB Galera Cluster with apt-get, follow the instructions at .
On SLES, OpenSUSE, and other similar Linux distributions, it is highly recommended to install the relevant from MariaDB's repository using .
To install MariaDB Galera Cluster with zypper, follow the instructions at .
To install MariaDB Galera Cluster with a binary tarball, follow the instructions at .
To make the location of the libgalera_smm.so library in binary tarballs more similar to its location in other packages, the library is now found at lib/galera/libgalera_smm.so in the binary tarballs, and there is a symbolic link in the lib directory that points to it.
To install MariaDB Galera Cluster by compiling it from source, you will have to compile both MariaDB Server and the Galera wsrep provider library. For some information on how to do this, see the pages at . The pages at and may also be helpful.
A number of options need to be set in order for Galera Cluster to work when using MariaDB. See for more information.
To first node of a new cluster needs to be bootstrapped by starting on that node with the option option. This option tells the node that there is no existing cluster to connect to. The node will create a new UUID to identify the new cluster.
Do not use the option when connecting to an existing cluster. Restarting the node with this option set will cause the node to create new UUID to identify the cluster again, and the node won't reconnect to the old cluster. See the next section about how to reconnect to an existing cluster.
For example, if you were manually starting on a node, then you could bootstrap it by executing the following:
However, keep in mind that most users are not going to be starting manually. Instead, most users will use a to start . See the following sections on how to bootstrap a node with the most common service managers.
On operating systems that use , a node can be bootstrapped in the following way:
This wrapper uses to run with the option.
If you are using the service that supports the , then you can bootstrap a specific instance by specifying the instance name as a suffix. For example:
Systemd support and the galera_new_cluster script were added.
On operating systems that use , a node can be bootstrapped in the following way:
This runs with the option.
Once you have a cluster running and you want to add/reconnect another node to it, you must supply an address of one or more of the existing cluster members in the option. For example, if the first node of the cluster has the address 192.168.0.1, then you could add a second node to the cluster by setting the following option in a server in an :
The new node only needs to connect to one of the existing cluster nodes. Once it connects to one of the existing cluster nodes, it will be able to see all of the nodes in the cluster. However, it is generally better to list all nodes of the cluster in , so that any node can join a cluster by connecting to any of the other cluster nodes, even if one or more of the cluster nodes are down. It is even OK to list a node's own IP address in , since Galera Cluster is smart enough to ignore it.
Once all members agree on the membership, the cluster's state will be exchanged. If the new node's state is different from that of the cluster, then it will request an IST or to make itself consistent with the other nodes.
If you shut down all nodes at the same time, then you have effectively terminated the cluster. Of course, the cluster's data still exists, but the running cluster no longer exists. When this happens, you'll need to bootstrap the cluster again.
If the cluster is not bootstrapped and on the first node is just started normally, then the node willl try to connect to at least one of the nodes listed in the option. If no nodes are currently running, then this will fail. Bootstrapping the first node solves this problem.
In some cases Galera will refuse to bootstrap a node if it detects that it might not be the most advanced node in the cluster. Galera makes this determination if the node was not the last one in the cluster to be shut down or if the node crashed. In those cases, manual intervention is needed.
If you know for sure which node is the most advanced you can edit the grastate.dat file in the . You can set safe_to_bootstrap=1 on the most advanced node.
You can determine which node is the most advanced by checking grastate.dat on each node and looking for the node with the highest seqno. If the node crashed and seqno=-1, then you can find the most advanced node by recovering the seqno on each node with the option. For example:
On operating systems that use , the position of a node can be recovered by running the galera_recovery script. For example:
If you are using the service that supports the , then you can recover the position of a specific instance by specifying the instance name as a suffix. For example:
The galera_recovery script recovers the position of a node by running with the option.
When the galera_recovery script runs , it does not write to the . Instead, it redirects log output to a file named with the format /tmp/wsrep_recovery.XXXXXX, where XXXXXX is replaced with random characters.
When Galera is enabled, MariaDB's service automatically runs the galera_recovery script prior to starting MariaDB, so that MariaDB starts with the proper Galera position.
Support for and the galera_recovery script were added.
In a State Snapshot Transfer (SST), the cluster provisions nodes by transferring a full data copy from one node to another. When a new node joins the cluster, the new node initiates a State Snapshot Transfer to synchronize its data with a node that is already part of the cluster.
See for more information.
In an Incremental State Transfer (SST), the cluster provisions nodes by transferring a node's missing writesets from one node to another. When a new node joins the cluster, the new node initiates a Incremental State Transfer to synchronize its data with a node that is already part of the cluster.
If a node has only been out of a cluster for a little while, then an IST is generally faster than an SST.
MariaDB Galera Cluster supports . See for some disclaimers on how SSTs are affected when encryption is configured.
Some data still cannot be encrypted:
The disk-based is not encrypted ().
can be queried with the standard command. For example:
The cluster nodes can be configured to invoke a command when cluster membership or node status changes. This mechanism can also be used to communicate the event to some external monitoring agent. This is configured by setting . See for more information.
This page is licensed: CC BY-SA / Gnu FDL
$ mariadbd --wsrep-new-cluster$ galera_new_cluster$ galera_new_cluster mariadb@node1$ service mysql bootstrap[mariadb]
...
wsrep_cluster_address=gcomm://192.168.0.1 # DNS names work as well, IP is preferred for performance$ mariadbd --wsrep_recover$ galera_recovery$ galera_recovery mariadb@node1SHOW GLOBAL STATUS LIKE 'wsrep_%';Articles on upgrading between MariaDB versions with Galera Cluster
The instructions on this page were used to create the galera package on the Ubuntu and Debian Linux distributions. This package contains the wsrep provider for MariaDB Galera Cluster.
The version of the wsrep provider is 25.3.5. We also provide 25.2.9 for those that need or want it. Prior to that, the wsrep version was 23.2.7.
Install prerequisites:
sudo apt-get update
sudo apt-get upgrade
sudo apt-get -y install check debhelper libasio-dev libboost-dev libboost-program-options-dev libssl-dev sconsClone galera.git from github.com/mariadb and checkout mariadb-3.x banch:
Build the packages by executing build.sh under scripts/ directory with -p switch:
When finished, you will have the Debian packages for galera library and arbitrator in the parent directory.
If you want to run the galera test suite (mysql-test-run --suite=galera), you need to install the galera library as either /usr/lib/galera/libgalera_smm.so or /usr/lib64/galera/libgalera_smm.so
This page is licensed: CC BY-SA / Gnu FDL
URLs in Galera take a particular format:
gcomm- This is the option to use for a working implementation.
dummy- Used for running tests and profiling, does not do any actual replication, and all following parameters are ignored.
The cluster address shouldn't be empty like gcomm://. This should never be hardcoded into any configuration files.
To connect the node to an existing cluster, the cluster address should contain the address of any member of the cluster you want to join.
The cluster address can also contain a comma-separated list of multiple members of the cluster. It is good practice to list all possible members of the cluster, for example. gcomm:<node1 name or ip>,<node2 name or ip2>,<node3 name or ip> Alternately, if multicast is used, put the multicast address instead of the list of nodes. Each member address or multicast address can specify <node name or ip>:<port>
The variable is used to set a . These parameters can also be provided (and overridden) as part of the URL. Unlike options provided in a configuration file, they will not endure and need to be resubmitted with each connection.
A useful option to set is pc.wait_prim=noto ensure the server will start running even if it can't determine a primary node. This is useful if all members go down at the same time.
By default, gcomm listens on all interfaces. The port is either provided in the cluster address or will default to 4567 if not set.
This page is licensed: CC BY-SA / Gnu FDL
The recommended strategy for creating a full, consistent backup of a MariaDB Galera Cluster is to perform the backup on a single . Because all nodes in a contain the same data, a complete backup from one node represents a snapshot of the entire cluster at a specific point in time.
The preferred tool for this is . mariadb-backup creates a "hot" backup without blocking the node from serving traffic for an extended period.
While taking a backup, the donor node is still receiving and applying transactions from the rest of the cluster. If the backup process is long, it's possible for the data at the end of the backup to be newer than the data at the
git init repo
cd repo
git clone -b mariadb-3.x https://github.com/MariaDB/galera.git<schema>://<cluster_address>[?option1=value1[&option2=value2]]cd galera
./scripts/build.sh -pTo prevent this, it's important to temporarily pause the node's replication stream during the backup process.
This procedure ensures a fully consistent backup with minimal impact on the cluster's availability.
Choose a node from your cluster to serve as the backup source. It's a good practice to use a non-primary node if you are directing writes to a single server.
To guarantee consistency, you should temporarily pause the node's ability to apply new replicated transactions. This is done by setting the wsrep_desync variable to ON.
Take the selected node out of your load balancer's rotation so it no longer receives application traffic.
Connect to the node with a mariadb client and execute:
The node will finish applying any transactions already in its queue and then pause, entering a "desynced" state. The rest of the cluster will continue to operate normally.
With the node's replication paused, run the mariadb-backup to create a full backup.
Once the backup is complete, you can allow the node to rejoin the cluster's replication stream.
Connect to the node again and execute:
The node will now request an Incremental State Transfer (IST) from its peers to receive all the transactions it missed while it was desynchronized and quickly catch up.
Once the node is fully synced (you can verify this by checking that wsrep_local_state_comment is Synced), add it back to your load balancer's rotation.
This procedure ensures you get a fully consistent snapshot of your cluster's data with zero downtime for your application.
This page is licensed: CC BY-SA / Gnu FDL
Auto-Eviction enhances cluster stability by automatically removing non-responsive or "unhealthy" nodes in MariaDB Galera Cluster. This prevents a single problematic node from degrading the entire cluster's performance. In a Galera Cluster, each node monitors the network response times of other nodes. If a node becomes unresponsive due to reasons like memory swapping, network congestion, or a hung process, it can delay and potentially disrupt cluster operations. Auto-Eviction provides a deterministic method to isolate these misbehaving nodes effectively.
The Auto-Eviction process is based on a consensus mechanism among the healthy cluster members.
Monitoring and Delay List: Each node in the cluster monitors the response times from all its peers. If a given node fails to respond within the expected timeframes, the other nodes will add an entry for it to their internal "delayed list."
Eviction Trigger: If a of the cluster nodes independently add the same peer to their delayed lists, it triggers the Auto-Eviction protocol.
Eviction: The cluster evicts the unresponsive node, removing it from the . The evicted node will enter a non-primary state and must be restarted to
The sensitivity of this process is determined by the evs.auto_evict parameter.
Auto-Eviction is configured by passing the evs.auto_evict within the wsrep_provider_options in your MariaDB configuration file (my.cnf).
The value of evs.auto_evict determines the threshold for eviction. It defines how many times a peer can be placed on the delayed list before the node votes to evict it.
In the above example example, if a node registers that a peer has been delayed 5 times, it will vote to have that peer evicted from the cluster.
To disable Auto-Eviction, you can set the value to 0:
Even when disabled, the node will continue to monitor response times and log information about delayed peers; it just won't vote to evict them.
The Auto-Eviction feature is directly related to the that control how the cluster detects unresponsive nodes in the first place. These parameters define what it means for a node to be "delayed."
Tuning these values in conjunction with evs.auto_evict allows you to define how aggressively the cluster will fence off struggling nodes.
This page is licensed: CC BY-SA / Gnu FDL
To facilitate development and QA, we have created some test repositories for the Galera wsrep provider.
These are test repositories. There will be periods when they do not work at all, or work incorrectly, or possibly cause earthquakes, typhoons, and tornadoes. You have been warned.
Replace ${dist} in the code below for
the YUM-based distribution you are testing. Valid distributions are:
centos5-amd64
centos5-x86
centos6-amd64
centos6-x86
Replace ${dist} in the code below
for the APT-based distribution
you are testing. Valid ones are:
wheezy
jessie
sid
precise
This page is licensed: CC BY-SA / Gnu FDL
Performing schema changes (i.e., Data Definition Language or DDL statements like ALTER TABLE, CREATE INDEX) in a MariaDB Galera Cluster requires special handling. Because Galera is a where all nodes must remain in sync, a schema change on one must be safely replicated to all other nodes without causing inconsistencies or blocking the entire cluster for an extended period.
MariaDB Galera Cluster provides two methods for handling schema upgrades:
SET GLOBAL wsrep_desync = ON;SET GLOBAL wsrep_desync = OFF;mariadb-backup --backup --target-dir=/path/to/backup/ --user=backup_user --password=...The method used is controlled by the wsrep_OSU_method session variable.
Total Order Isolation is the default method for schema upgrades (wsrep_OSU_method = 'TOI'). It ensures maximum data consistency by treating the DDL statement like any other transaction that must be applied in the same order on all nodes.
When you execute a DDL statement, such as ALTER TABLE..., on any node in a cluster, the following process occurs:
Replication: The statement is replicated across all nodes in the cluster.
Transaction Wait: Each node waits for any pre-existing transactions to complete before proceeding.
Execution: Once caught up, the node executes the DDL statement.
Resume Processing: After execution, the node can process new transactions.
Simplicity and Safety: It is the easiest and safest method. It guarantees that the schema is identical on all nodes at all times.
Consistency: There is no risk of data drifting or replication errors due to schema mismatches.
A major drawback of DDL statements is that they block the entire cluster, preventing any node from processing write transactions during a schema change. This can lead to significant application downtime, especially for large tables that take a long time to alter.
TOI is the recommended method for:
Schema changes that are known to be very fast.
Environments where a short period of cluster-wide write unavailability is acceptable.
Situations where schema consistency is the absolute highest priority.
Rolling Schema Upgrade is a non-blocking method (wsrep_OSU_method = 'RSU') that allows you to perform schema changes without taking the entire cluster offline.
The RSU method tells the cluster to not replicate the DDL statement. The change is only applied to the local node where you execute the command. It is then the administrator's responsibility to apply the same change to the other nodes one by one.
Set the RSU Method:
On the first node, set the session to RSU mode:
SET SESSION wsrep_OSU_method = 'RSU';
Remove the Node from Rotation: Remove the node from the load balancer to stop it from receiving traffic.
Apply the Schema Change:
Execute the DDL statement (e.g., ALTER TABLE...) on the isolated node.
Return the Node to Rotation:
Once the ALTER statement is complete, add the node back to the load balancer.
Repeat for All Nodes: Repeat steps 1-4 for each node in the cluster, one at a time, until all nodes have the updated schema.
High Availability: The cluster remains online and available to serve traffic throughout the entire process, as you only ever take one node out of rotation at a time.
No Cluster-Wide Blocking: Application writes can continue on the active nodes.
Complexity and Risk: The process is manual and more complex, which introduces a higher risk of human error.
Temporary Inconsistency: For the duration of the upgrade, your cluster will have a mixed schema, where some nodes have the old schema and others have the new one. This can cause replication errors if a transaction that relies on the new schema is sent to a node that has not yet been upgraded.
RSU is the best method for:
Applying long-running schema changes to large tables where cluster downtime is not acceptable.
Environments where high availability is the top priority.
It requires careful planning and a good understanding of your application's queries to ensure that no replication errors occur during the upgrade process.
This page is licensed: CC BY-SA / Gnu FDL
Total Order Isolation (TOI)
Default and safest method. The DDL statement is replicated to all nodes, blocking the entire cluster until all preceding transactions complete.
Rolling Schema Upgrade (RSU)
Advanced, non-blocking method. The DDL is executed on the local node, with changes applied manually to each node in sequence, keeping the cluster online.
Frequency of node checking for inactive peers.
Time duration after which a non-responsive node is marked as "suspect."
Time duration after which a non-responsive node is marked as "inactive" and removed.
centos7-amd64
rhel5-amd64
rhel5-x86
rhel6-amd64
rhel6-x86
rhel6-ppc64
rhel7-amd64
rhel7-ppc64
rhel7-ppc64le
fedora22-amd64
fedora22-x86
fedora23-amd64
fedora23-x86
fedora24-amd64
fedora24-x86
opensuse13-amd64
opensuse13-x86
sles11-amd64
sles11-x86
sles12-amd64
sles12-ppc64le
trusty
xenial
[mariadb]
...
wsrep_provider_options = "evs.auto_evict=5"wsrep_provider_options = "evs.auto_evict=0"[galera-test]
name = galera-test
baseurl = http://yum.mariadb.org/galera/repo/rpm/${dist}
gpgkey=https://yum.mariadb.org/RPM-GPG-KEY-MariaDB
gpgcheck=1# run the following command:
sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 0xcbcb082a1bb943db 0xF1656F24C74CD1D8
# Add the following line to your /etc/apt/sources.list file:
deb http://yum.mariadb.org/galera/repo/deb ${dist} mainGalera Cluster ships with the MariaDB Server. Upgrading a Galera Cluster node is very similar to upgrading a server from MariaDB 10.4 to MariaDB 10.5. For more information on that process as well as incompatibilities between versions, see the .
The following steps can be used to perform a rolling upgrade from MariaDB 10.4 to MariaDB 10.5 when using Galera Cluster. In a rolling upgrade, each node is upgraded individually, so the cluster is always operational. There is no downtime from the application's perspective.
First, before you get started:
First, take a look at to see what has changed between the major versions.
Check whether any system variables or options have been changed or removed. Make sure that your server's configuration is compatible with the new MariaDB version before upgrading.
Check whether replication has changed in the new MariaDB version in any way that could cause issues while the cluster contains upgraded and non-upgraded nodes.
Check whether any new features have been added to the new MariaDB version. If a new feature in the new MariaDB version cannot be replicated to the old MariaDB version, then do not use that feature until all cluster nodes have been upgrades to the new MariaDB version.
Next, make sure that the Galera version numbers are compatible.
If you are upgrading from the most recent release to , then the versions will be compatible.
See ?: s for information on which MariaDB releases uses which Galera wsrep provider versions.
You want to have a large enough gcache to avoid a during the rolling upgrade. The gcache size can be configured by setting For example:wsrep_provider_options="gcache.size=2G"
Before you upgrade, it would be best to take a backup of your database. This is always a good idea to do before an upgrade. We would recommend .
Then, for each node, perform the following steps:
Modify the repository configuration, so the system's package manager installs
see for more information.
see for more information.
see for more information.
When this process is done for one node, move onto the next node.
When upgrading the Galera wsrep provider, sometimes the Galera protocol version can change. The Galera wsrep provider should not start using the new protocol version until all cluster nodes have been upgraded to the new version, so this is not generally an issue during a rolling upgrade. However, this can cause issues if you restart a non-upgraded node in a cluster where the rest of the nodes have been upgraded.
This page is licensed: CC BY-SA / Gnu FDL
There are binary installation packages available for RPM and Debian-based distributions, which will pull in all required Galera dependencies.
If these are not available, you will need to build Galera from source.
The wsrep API for Galera Cluster is included by default. Follow the usual instructions
make cannot manage dependencies for the build process, so the following packages need to be installed first:
RPM-based:
Debian-based:
If running on an alternative system, or the commands are available, the following packages are required. You will need to check the repositories for the correct package names on your distribution—these may differ between distributions or require additional packages:
Git, CMake (on Fedora, both cmake and cmake-fedora are required), GCC and GCC-C++, Automake, Autoconf, and Bison, as well as development releases of libaio and ncurses.
You can use Git to download the source code, as MariaDB source code is available through GitHub. 1. Clone the repository:
Check out the branch (e.g., 10.5-galera or 11.1-galera), for example:
The standard and Galera Cluster database servers are the same, except that for Galera Cluster, the wsrep API patch is included. Enable the patch with the CMake configuration options. WITH_WSREP and WITH_INNODB_DISALLOW_WRITES. To build the database server, run the following commands:
There are also some build scripts in the *BUILD/* directory, which may be more convenient to use. For example, the following pre-configures the build options discussed above:
There are several others as well, so you can select the most convenient.
<>
Besides the server with the Galera support, you will also need a Galera provider.
make cannot manage dependencies itself, so the following packages need to be installed first:
If running on an alternative system, or the commands are available, the following packages are required. You will need to check the repositories for the correct package names on your distribution - these may differ between distributions, or require additional packages:
SCons, as well as development releases of Boost (libboost_program_options, libboost_headers1), Check and OpenSSL.
Run:
After this, the source files for the Galera provider will be in the galera directory.
The Galera Replication Plugin both implements the wsrep API and operates as the database server's wsrep Provider. To build, cd into the galera/ directory and do:
The path to libgalera_smm.so needs to be defined in the my.cnf configuration file.
Building Galera Replication Plugin from source on FreeBSD runs into issues due to Linux dependencies. To overcome these, either install the binary package: pkg install galera, or use the ports build available at /usr/ports/databases/galera.
After building, a number of other steps are necessary:
Create the database server user and group:
Install the database (the path may be different if you specified CMAKE_INSTALL_PREFIX):
If you want to install the database in a location other than /usr/local/mysql/data , use the --basedir or --datadir options.
Change the user and group permissions for the base directory.
Create a system unit for the database server.
Galera Cluster can now be started using the service command and is set to start at boot.
This page is licensed: CC BY-SA / Gnu FDL
allows for the generation of unique integers independent of any specific table. While standard sequences function normally in a standalone MariaDB server, using them in a MariaDB Galera Cluster requires specific configurations to ensure conflict-free operation and optimal performance.
Starting from MariaDB 10.11.16 (and Galera 26.4.16), sequences are fully supported in transactions utilizing streaming replication. In earlier versions, using NEXTVAL() within a transaction where wsrep_trx_fragment_size > 0 would cause an ERROR 1235. The WSREP API now ensures proper serialization of sequence state in transaction fragments, allowing sequences to be used effectively in large-scale ETL and batch operations. See MDEV-34124
Because Galera is a multi-primary system, multiple nodes may attempt to generate sequence values simultaneously. To prevent duplicate values and certification failures, the cluster utilizes an offset-based generation strategy.
For a sequence to function correctly in a multi-node environment, it must be defined with INCREMENT BY 0.
This setting instructs the node to ignore the sequence's internal increment logic. Instead, the node applies the cluster-wide wsrep_auto_increment_control logic using the following formula:
Where:
Node_Offset: The unique identifier for the specific node (e.g., 1, 2, or 3).
Cluster_Size: The total number of nodes in the cluster.
N: The iteration count (0, 1, 2, ...).
Visualizing the Offset Logic
The following diagram illustrates how two nodes in a 3-node cluster generate unique IDs simultaneously without communicating or locking.
This ensures that nodes generate interleaved, non-conflicting IDs preventing Certification Failures (Error 1213) without requiring network locks.
The CACHE option is the primary lever for balancing performance against data continuity. In Galera, replication introduces a "Flush-on-Sync" behavior: when any node commits a sequence update, other nodes must sync their state, discarding any unused values in their local cache.
A common requirement for Galera is a distributed system (e.g., ticket sales) where users in different regions must be able to book items simultaneously without "race conditions" or duplicate Booking IDs.
In this example, we configure a sequence to allow high-speed concurrent bookings from multiple nodes.
This page is licensed: CC BY-SA / Gnu FDL
Galera Cluster ships with the MariaDB Server. Upgrading a Galera Cluster node is very similar to upgrading a server from to . For more information on that process as well as incompatibilities between versions, see the .
The following steps can be used to perform a rolling upgrade from to when using Galera Cluster. In a rolling upgrade, each node is upgraded individually, so the cluster is always operational. There is no downtime from the application's perspective.
First, before you get started:
First, take a look at to see what has changed between the major versions.
Check whether any system variables or options have been changed or removed. Make sure that your server's configuration is compatible with the new MariaDB version before upgrading.
Check whether replication has changed in the new MariaDB version in any way that could cause issues while the cluster contains upgraded and non-upgraded nodes.
Check whether any new features have been added to the new MariaDB version. If a new feature in the new MariaDB version cannot be replicated to the old MariaDB version, then do not use that feature until all cluster nodes have been upgrades to the new MariaDB version.
Next, make sure that the Galera version numbers are compatible.
If you are upgrading from the most recent release to , then the versions will be compatible.
See ?: for information on which MariaDB releases uses which Galera wsrep provider versions.
You want to have a large enough gcache to avoid a during the rolling upgrade. The gcache size can be configured by setting for example:wsrep_provider_options="gcache.size=2G"
Before you upgrade, it would be best to take a backup of your database. This is always a good idea to do before an upgrade. We would recommend .
Then, for each node, perform the following steps:
Modify the repository configuration, so the system's package manager installs
see for more information.
see for more information.
see for more information.
When this process is done for one node, move onto the next node.
When upgrading the Galera wsrep provider, sometimes the Galera protocol version can change. The Galera wsrep provider should not start using the new protocol version until all cluster nodes have been upgraded to the new version, so this is not generally an issue during a rolling upgrade. However, this can cause issues if you restart a non-upgraded node in a cluster where the rest of the nodes have been upgraded.
This page is licensed: CC BY-SA / Gnu FDL
Flow Control is a key feature in MariaDB Galera Cluster that ensures nodes remain synchronized. In synchronous replication, no node should lag significantly in processing transactions.
Flow Control manages this by aligning all nodes' replication processes:
Without Flow Control, a slow node's replication queue can grow unchecked, consuming all server memory and potentially crashing the MariaDB process due to an Out-Of-Memory (OOM) error.
It maintains synchronization across the cluster, ensuring all nodes have nearly identical database states at all times.
The Flow Control process is an automatic feedback loop triggered by the state of a node's replication queue.
Queue Growth: A node (the "slow node") begins receiving from its peers faster than it can apply them. This causes its local receive queue, measured by the wsrep_local_recv_queue , to grow.
Upper Limit Trigger: When the receive queue size exceeds the configured upper limit, defined by the gcs.fc_limit , the slow node triggers Flow Control.
Pause Message: The node broadcasts a "Flow Control PAUSE" message to all other nodes in the cluster.
As an administrator, observing Flow Control is a key indicator of a performance bottleneck in your cluster. You can monitor it using the following global :
If you observe frequent Flow Control pauses, it is essential to identify and address the underlying cause.
These my.cnf control the sensitivity of Flow Control:
Modifying these values is an advanced tuning step. In most cases, it is better to fix the underlying cause of the bottleneck rather than relaxing the Flow Control limits.
This page is licensed: CC BY-SA / Gnu FDL
MariaDB starting with
Since , the patch has been merged into MariaDB Server. Therefore, in and above, the functionality of MariaDB Galera Cluster can be obtained by installing the standard MariaDB Server packages and the Galera wsrep provider library package.
Beginning in , ships with the MariaDB Server. Upgrading a Galera Cluster node is very similar to upgrading a server from to . For more information on that process as well as incompatibilities between versions, see the .
Streaming Replication optimizes replication of large or long-running transactions in MariaDB Galera Cluster. Typically, a node executes a transaction fully and replicates the complete to other nodes at time. Although efficient for most workloads, this approach can be challenging for very large or lengthy transactions.
With Streaming Replication, the initiating node divides the transaction into smaller fragments. These fragments are certified and replicated to other nodes while the transaction is ongoing. Once a fragment is certified and applied to the replicas, it becomes immune to abortion by conflicting transactions, thus improving the chances of the entire transaction succeeding. This method also supports processing of transaction write-sets over two Gigabytes.
MariaDB Galera Cluster provides a powerful automation feature through the wsrep_notify_cmd . When this variable is configured, the MariaDB server will automatically execute a specified command or script in response to changes in the cluster's membership or the local node's state.
This is extremely useful for integrating the cluster with external systems:
yum-builddep MariaDB-serverapt-get build-dep mariadb-serverIf you use a load balancing proxy such as or HAProxy, make sure to drain the server from the pool so it does not receive any new connections.
.
Uninstall the old version of MariaDB and the Galera wsrep provider.
sudo apt-get remove mariadb-server galerasudo yum remove MariaDB-server galerasudo zypper remove MariaDB-server galeraInstall the new version of MariaDB and the Galera wsrep provider.
see for more information.
see for more information.
see for more information.
Make any desired changes to configuration options in , such as my.cnf. This includes removing any system variables or options that are no longer supported.
On Linux distributions that use systemd you may need to increase the service startup timeout as the default timeout of 90 seconds may not be sufficient. See for more information.
.
Run with the --skip-write-binlog option.
mysql_upgrade does two things:
Ensures that the system tables in the database are fully compatible with the new version.
Does a very quick check of all tables and marks them as compatible with the new version of MariaDB.
If you use a load balancing proxy such as or HAProxy, make sure to drain the server from the pool so it does not receive any new connections.
.
Uninstall the old version of MariaDB and the Galera wsrep provider.
sudo apt-get remove mariadb-server galerasudo yum remove MariaDB-server galerasudo zypper remove MariaDB-server galeraInstall the new version of MariaDB and the Galera wsrep provider.
see for more information.
see for more information.
see for more information.
Make any desired changes to configuration options in , such as my.cnf. This includes removing any system variables or options that are no longer supported.
On Linux distributions that use systemd you may need to increase the service startup timeout as the default timeout of 90 seconds may not be sufficient. See for more information.
.
Run with the --skip-write-binlog option.
mysql_upgrade does two things:
Ensures that the system tables in the database are fully compatible with the new version.
Does a very quick check of all tables and marks them as compatible with the new version of MariaDB.
Replication Pauses: Upon receiving this message, all nodes in the cluster temporarily stop replicating new transactions. They continue to process any transactions already in their queues.
Queue Clears: The slow node now has a chance to catch up and apply the transactions from its backlog without new ones arriving.
Lower Limit Trigger: When the node's receive queue size drops below a lower threshold (defined as gcs.fc_limit * gcs.fc_factor), the node broadcasts a "Flow Control RESUME" message.
Replication Resumes: The entire cluster resumes normal replication.
Indicates the fraction of time since the last FLUSH STATUS that the node has been paused by Flow Control. A value near 0.0 is healthy; 0.2 or higher indicates issues.
Represents the average size of the receive queue. A high or increasing value suggests a node struggling to keep up, likely triggering Flow Control.
Counter for the number of "PAUSE" messages a node has sent. A high value indicates the node causing the cluster to pause.
Counter for the number of "PAUSE" messages a node has received.
Maximum number of write-sets allowed in the receive queue before Flow Control is triggered.
100
Decimal value used to determine the "resume" threshold. The queue must shrink to gcs.fc_limit * gcs.fc_factor before replication resumes.
0.8
One node is slower due to mismatched hardware, higher network latency, or competing workloads.
Investigate and either upgrade the node's resources or move the workload.
Insufficient Applier Threads
Galera may not utilize enough parallel threads, leading to bottlenecks on multi-core servers.
Increase wsrep_slave_threads according to your server's CPU core count.
Large , , or statements can create large write-sets, slowing down application by other nodes.
Break large data modification operations into smaller batches.
Workload Contention
Long-running queries on can create locks that prevent replication, causing receive queues to grow.
Optimize read queries and consider wsrep_sync_wait for consistent read-after-write checks to avoid long locks on resources needed for replication.
First, before you get started:
First, take a look at to see what has changed between the major versions.
Check whether any system variables or options have been changed or removed. Make sure that your server's configuration is compatible with the new MariaDB version before upgrading.
Check whether replication has changed in the new MariaDB version in any way that could cause issues while the cluster contains upgraded and non-upgraded nodes.
Check whether any new features have been added to the new MariaDB version. If a new feature in the new MariaDB version cannot be replicated to the old MariaDB version, then do not use that feature until all cluster nodes have been upgrades to the new MariaDB version.
Next, make sure that the Galera version numbers are compatible.
If you are upgrading from the most recent release to , then the versions will be compatible. uses Galera 3 (i.e. Galera wsrep provider versions 25.3.x), and uses Galera 4 (i.e. Galera wsrep provider versions 26.4.x). This means that upgrading to also upgrades the system to Galera 4. However, Galera 3 and Galera 4 should be compatible for the purposes of a rolling upgrade, as long as you are using Galera 26.4.2 or later.
See ? for information on which MariaDB releases uses which Galera wsrep provider versions.
Ideally, you want to have a large enough gcache to avoid a during the rolling upgrade. The gcache size can be configured by setting For example:wsrep_provider_options="gcache.size=2G"
Before you upgrade, it would be best to take a backup of your database. This is always a good idea to do before an upgrade. We would recommend .
Then, for each node, perform the following steps:
Modify the repository configuration, so the system's package manager installs .
see for more information.
see for more information.
see for more information.
If you use a load balancing proxy such as MaxScale or HAProxy, make sure to drain the server from the pool so it does not receive any new connections.
.
Uninstall the old version of MariaDB and the Galera wsrep provider.
Install the new version of MariaDB and the Galera wsrep provider.
see for more information.
see for more information.
see for more information.
Make any desired changes to configuration options in , such as my.cnf. This includes removing any system variables or options that are no longer supported.
On Linux distributions that use systemd you may need to increase the service startup timeout as the default timeout of 90 seconds may not be sufficient. See for more information.
.
Run with the --skip-write-binlog option.
mysql_upgrade does two things:
Ensures that the system tables in the l database are fully compatible with the new version.
When this process is done for one node, move onto the next node.
When upgrading the Galera wsrep provider, sometimes the Galera protocol version can change. The Galera wsrep provider should not start using the new protocol version until all cluster nodes have been upgraded to the new version, so this is not generally an issue during a rolling upgrade. However, this can cause issues if you restart a non-upgraded node in a cluster where the rest of the nodes have been upgraded.
This page is licensed: CC BY-SA / Gnu FDL
In most cases, the standard replication method is sufficient. Streaming Replication is a specialized tool for specific scenarios. The best practice is to enable it only at the session level for the specific transactions that require it.
This is the primary use case. When performing a massive , , or , normal replication requires the originating node to hold the entire transaction locally and then send a very large write-set at commit time. This can cause two problems:
A significant replication lag, as the entire cluster waits for the large write-set to be transferred and applied.
The replica nodes, while busy applying the large transaction, cannot commit other transactions, which can trigger Flow Control and throttle the entire cluster.
With Streaming Replication, the node replicates the data in fragments throughout the transaction's lifetime. This spreads the network load and allows replica nodes to apply other concurrent transactions between fragments, minimizing the impact on the overall cluster performance.
A transaction that remains open for a long time has a higher chance of conflicting with a smaller, faster transaction that commits first. When this happens, the long-running transaction is aborted.
Streaming Replication mitigates this by committing the transaction in fragments. Once a fragment is certified, it is "locked in" and cannot be aborted by a new conflicting transaction.
Certification keys derive from record locks, not gap locks. If a streaming transaction holds a gap lock, another node's transaction can still apply a write-set in that gap, potentially aborting the streaming transaction.
For applications that frequently update the same row (e.g., a counter, a job queue, or a locking scheme), Streaming Replication can be used to force a critical update to replicate immediately. This effectively locks the "hot record" on all nodes, preventing other transactions from modifying it and increasing the chance that the critical transaction will commit successfully.
Streaming Replication should be enabled at the session level just for the transactions that need it. This is controlled by two session variables:
wsrep_trx_fragment_unit defines what a "unit" of replication is.
wsrep_trx_fragment_size defines how many units make up a fragment.
To enable streaming, you set both variables:
In the above example, the node will create, certify, and replicate a fragment after every 10 SQL statements within the transaction.
The available fragment units for wsrep_trx_fragment_unit are:
bytes
The fragment size is defined in bytes of the write-set.
rows
The fragment size is defined by the number of rows affected.
statements
The fragment size is defined by the number of SQL statements executed.
To disable Streaming Replication, you can set wsrep_trx_fragment_size back to 0.
Consider an application that manages a work order queue. To prevent two users from getting the same queue position, you can use Streaming Replication for the single critical update.
Begin the transaction:
After reading necessary data, enable Streaming Replication for just the next statement:
Perform the critical update. This statement will be immediately fragmented and replicated:
Immediately disable Streaming Replication for the rest of the transaction:
Perform other, non-critical tasks for the work order, and then commit:
This ensures the queue_position update is replicated and certified across the cluster before the rest of the transaction proceeds, preventing race conditions.
Before using Streaming Replication, consider the following limitations:
When Streaming Replication is enabled, Galera records all write-sets to a log table (mysql.wsrep_streaming_log) on every node to ensure persistence in case of a crash. This adds write overhead and can impact performance, which is why it should only be used when necessary.
If a streaming transaction needs to be rolled back after some fragments have already been applied, the rollback operation consumes system resources on all nodes as they undo the previously applied fragments. Frequent rollbacks of streaming transactions can become a performance problem.
For these reasons, it is always a good application design policy to use shorter, smaller transactions whenever possible.
This page is licensed: CC BY-SA / Gnu FDL
Rolling upgrade with IST (however, see MDEV-33263)
Note that rolling upgrade with SST does not work
The following steps can be used to perform a rolling upgrade from to when using Galera Cluster. In a rolling upgrade, each node is upgraded individually, so the cluster is always operational. There is no downtime from the application's perspective.
First, before you get started:
First, take a look at to see what has changed between the major versions.
Check whether any system variables or options have been changed or removed. Make sure that your server's configuration is compatible with the new MariaDB version before upgrading.
Check whether replication has changed in the new MariaDB version in any way that could cause issues while the cluster contains upgraded and non-upgraded nodes.
Check whether any new features have been added to the new MariaDB version. If a new feature in the new MariaDB version cannot be replicated to the old MariaDB version, then do not use that feature until all cluster nodes have been upgrades to the new MariaDB version.
Next, make sure that the Galera version numbers are compatible.
If you are upgrading from the most recent release to , then the versions will be compatible.
See ?: for information on which MariaDB releases uses which Galera wsrep provider versions.
You want to have a large enough gcache to avoid a during the rolling upgrade. The gcache size can be configured by setting For example:wsrep_provider_options="gcache.size=2G"
Before you upgrade, it would be best to take a backup of your database. This is always a good idea to do before an upgrade. We would recommend .
Then, for each node, perform the following steps:
Modify the repository configuration, so the system's package manager installs
see for more information.
see for more information.
see for more information.
If you use a load balancing proxy such as or HAProxy, make sure to drain the server from the pool so it does not receive any new connections.
.
Uninstall the old version of MariaDB and the Galera wsrep provider.
Install the new version of MariaDB and the Galera wsrep provider.
see for more information.
see for more information.
see for more information.
Make any desired changes to configuration options in , such as my.cnf. This includes removing any system variables or options that are no longer supported.
On Linux distributions that use systemd you may need to increase the service startup timeout as the default timeout of 90 seconds may not be sufficient. See for more information.
.
Run with the --skip-write-binlog option.
mysql_upgrade does two things:
Ensures that the system tables in the database are fully compatible with the new version.
Does a very quick check of all tables and marks them as compatible with the new version of MariaDB.
When this process is done for one node, move onto the next node.
When upgrading the Galera wsrep provider, sometimes the Galera protocol version can change. The Galera wsrep provider should not start using the new protocol version until all cluster nodes have been upgraded to the new version, so this is not generally an issue during a rolling upgrade. However, this can cause issues if you restart a non-upgraded node in a cluster where the rest of the nodes have been upgraded.
This page is licensed: CC BY-SA / Gnu FDL
To use this feature, you set the wsrep_notify_cmd variable in your MariaDB configuration file (my.cnf) to the full path of the script you want to execute:
The MariaDB server user must have the permissions for the specified script.
When a cluster event occurs, the server executes the configured script and passes several arguments to it, providing context about the event. The script can then use these arguments to take appropriate action.
The script is called with the following parameters:
$1
Status
The new status of the node (e.g., Synced, Donor).
$2
View ID
A unique identifier for the current cluster membership view.
$3
Members List
A comma-separated list of the names of all members in the current view.
$4
Is Primary
The first argument indicates the new state of the local node. The most common values are:
Joining: The node is starting to join the cluster.
Joined: The node has finished a state transfer and is catching up.
Synced: The node is a fully operational member of the cluster.
Donor: The node is currently providing a State Snapshot Transfer (SST).
Desynced: The node has been manually desynchronized (wsrep_desync=ON).
The View ID is a unique identifier composed of the view sequence number and the UUID of the node that initiated the view change. It changes every time a node joins or leaves the cluster.
The third argument is a comma-separated list of the wsrep_node_name of every member in the current cluster component.
Your script can parse this list to get a complete, real-time picture of the cluster's membership.
Here is a simple example of a bash script that logs all cluster state changes to a file.
notify_script.sh:
This script would provide a simple, human-readable log of all membership and node state changes, which can be invaluable for troubleshooting.
This page is licensed: CC BY-SA / Gnu FDL
Automatically add or remove nodes from the load balancer's pool as they join or leave the cluster.
Send custom alerts to a monitoring system when a node's status changes.
Service Discovery
Update a service discovery tool with the current list of active cluster members.
CACHE 1
High Concurrency
Recommended for multi-primary writes. Disables pre-allocation. Every NEXTVAL() triggers a commit and flush. No values are lost during sync, ensuring continuity, but at the cost of higher I/O and latency.
CACHE 1000
Single Writer
Recommended for write-heavy single nodes. Allows the writer node to batch updates to disk, offering performance similar to a standalone server. However, if a secondary node writes to the sequence, the primary node's cache is discarded, creating gaps.
CACHE 50
Hybrid
A balanced approach. Reduces disk flushes significantly compared to CACHE 1 while limiting the size of potential gaps during occasional concurrent writes.
ERROR 1235 ... doesn't yet support SEQUENCEs
The server version is older than 10.11.16 and Streaming Replication is enabled.
Upgrade to a supported version or disable Streaming Replication (SET SESSION wsrep_trx_fragment_size=0).
ERROR 1213: Deadlock found when trying to get lock
The sequence was likely defined with INCREMENT BY 1 (default), causing nodes to contend for the same value.
Alter the sequence to use the Galera offset logic: ALTER SEQUENCE my_seq INCREMENT BY 0;
A number of options need to be set in order for Galera Cluster to work when using MariaDB. These should be set in the MariaDB option file.
Several options are mandatory, which means that they must be set in order for Galera Cluster to be enabled or to work properly with MariaDB. The mandatory options are:
wsrep_provider — Path to the Galera library
— See
— See
— Enable wsrep replication
— This is the default value, or alternately (before MariaDB 10.6) or (MariaDB 10.6 and later).
— This is the default value, and should not be changed.
These are optional optimizations that can be made to improve performance.
— This is not usually recommended in the case of standard MariaDB. However, it is a safer, recommended option with Galera Cluster, since inconsistencies can always be fixed by recovering from another node.
— This tells InnoDB to use interleaved method. Interleaved is the fastest and most scalable lock mode, and should be used when BINLOG_FORMAT is set to ROW. Setting the auto-increment lock mode for InnoDB to interleaved, you’re allowing slaves threads to operate in parallel.
— This makes state transfers quicker for new nodes. You should start with four slave threads per CPU core. The logic here is that, in a balanced system, four slave threads can typically saturate a CPU core. However, I/O performance can increase this figure several times over. For example, a single-core ThinkPad R51 with a 4200 RPM drive can use thirty-two slave threads. The value should not be set higher than .
Like with , write sets that are received by a node with are not written to the by default. If you would like a node to write its replicated write sets to the , then you will have to set . This is especially helpful if the node is a replication master. See .
Like with , can be used to filter write sets from being replicated by . However, they should be used with caution because they may not work as you'd expect.
The following replication filters are honored for DML, but not DDL:
The following replication filters are honored for DML and DDL for tables that use both the and storage engines:
However, it should be kept in mind that if replication filters cause inconsistencies that lead to replication errors, then nodes may abort.
See also and .
Galera Cluster needs access to the following ports:
Standard MariaDB Port (default: 3306) - For MySQL client connections and that use the mysqldump method. This can be changed by setting .
Galera Replication Port (default: 4567) - For Galera Cluster replication traffic, multicast replication uses both UDP transport and TCP on this port. Can be changed by setting .
Galera Replication Listening Interface (default: 0.0.0.0:4567) needs to be set using , either
If you want to run multiple Galera Cluster instances on one server, then you can do so by starting each instance with , or if you are using , then you can use the relevant .
You need to ensure that each instance is configured with a different .
You also need to ensure that each instance is configured with different .
This page is licensed: CC BY-SA / Gnu FDL
Get MariaDB Galera on IBM Cloud
You should have an IBM Cloud account; otherwise, you can . At the end of the tutorial, you will have a cluster with MariaDB up and running. IBM Cloud uses Bitnami charts to deploy MariaDB Galera with Helm
We will provision a new Kubernetes Cluster for you if, you already have one, skip to step 2
We will deploy the IBM Cloud Block Storage plug-in; if you already have it, skip to step 3
START TRANSACTION;SET SESSION wsrep_trx_fragment_unit = 'statements';
SET SESSION wsrep_trx_fragment_size = 1;UPDATE work_orders
SET queue_position = queue_position + 1;SET SESSION wsrep_trx_fragment_size = 0;SET SESSION wsrep_trx_fragment_unit = 'statements';
SET SESSION wsrep_trx_fragment_size = 10;[mariadb]
...
wsrep_notify_cmd = /path/to/your/script.shgalera1,galera2,galera3#!/bin/bash
# Define the log file
LOG_FILE="/var/log/galera_events.log"
# Arguments passed by Galera
STATUS="$1"
VIEW_ID="$2"
MEMBERS="$3"
IS_PRIMARY="$4"
# Get the current timestamp
TIMESTAMP=$(date +"%Y-%m-%d %T")
# Log the event
echo "${TIMESTAMP}: Node status changed to ${STATUS}. View ID: ${VIEW_ID}. Members: [${MEMBERS}]. Is Primary: ${IS_PRIMARY}" >> "${LOG_FILE}"
exit 0git clone https://github.com/mariadb/server mariadbcd mariadb
git checkout 10.5-galeracmake -DWITH_WSREP=ON -DWITH_INNODB_DISALLOW_WRITES=ON .
make
make install./BUILD/compile-pentium64-wsrepapt-get install -y scons checkgit clone -b mariadb-4.x https://github.com/MariaDB/galera.gitgit submodule init
git submodule update
./scripts/build.sh
mkdir /usr/lib64/galera
cp libgalera_smm.so /usr/lib64/galeragroupadd mysql
useradd -g mysql mysqlcd /usr/local/mysql
./scripts/mariadb-install-db --user=mysqlchown -R mysql /usr/local/mysql
chgrp -R mysql /usr/local/mysqlcp /usr/local/mysql/supported-files/mysql.server /etc/init.d/mysql
chmod +x /etc/init.d/mysql
chkconfig --add mysqlCREATE SEQUENCE seq_tickets START WITH 1 INCREMENT BY 0;-- 1. Create a sequence optimized for concurrent access
-- CACHE 1 ensures no IDs are skipped if customers bounce between nodes
CREATE SEQUENCE seq_booking_id START WITH 1000 INCREMENT BY 0 CACHE 1;
-- 2. The Application Logic (Run on Node A or Node B)
START TRANSACTION;
-- Generate a unique Booking ID instantly (No cluster lock needed)
SELECT NEXTVAL(seq_booking_id) INTO @new_id;
-- Insert the reservation
INSERT INTO bookings (id, customer, event)
VALUES (@new_id, 'Jane Doe', 'Concert 2025');
COMMIT;A boolean indicating if the current component is the Primary Component (1 for true, 0 for false).
in wsrep_provider_options: wsrep_provider_options='gmcast.listen_addr=tcp://<IP_ADDR>:<PORT>;'
or in wsrep_cluster_address
IST Port (default: 4568) - For Incremental State Transfers. Can be changed by setting ist.recv_addr in wsrep_provider_options.
SST Port (default: 4444) - For all State Snapshot Transfer methods other than mysqldump. Can be changed by setting wsrep_sst_receive_address.
Click the Catalog button on the top
Select Service from the catalog
Search for Kubernetes Service and click on it
You are now at the Kubernetes deployment page; you need to specify some details about the cluster
Choose a standard or free plan; the free plan only has one worker node and no subnet. to provision a standard cluster, you will need to upgrade account to Pay-As-You-Go
To upgrade to a Pay-As-You-Go account, complete the following steps:
In the console, go to Manage > Account.
Select Account settings, and click Add credit card.
Enter your payment information, click Next, and submit your information
Choose classic or VPC, read the , and choose the most suitable type for yourself
Now choose your location settings; for more information, please visit Locations
Choose Geography (continent)
Choose Single or Multizone. In single zone, your data is only kept in one datacenter; on the other hand, with Multizone it is distributed to multiple zones, thus safer in an unforeseen zone failure
Choose a Worker Zone if using Single zones or Metro if Multizone
If you wish to use Multizone please set up your account with VRF or enable Vlan spanning
If at your current location selection, there is no available Virtual LAN, a new Vlan will be created for you
Choose a Worker node setup or use the preselected one, set Worker node amount per zone
Choose Master Service Endpoint, In VRF-enabled accounts, you can choose private-only to make your master accessible on the private network or via VPN tunnel. Choose public-only to make your master publicly accessible. When you have a VRF-enabled account, your cluster is set up by default to use both private and public endpoints. For more information visit endpoints.
Give cluster a name
Give desired tags to your cluster; for more information, visit tags
Click create
Wait for you cluster to be provisioned
Your cluster is ready for usage
The Block Storage plug-in is a persistent, high-performance iSCSI storage that you can add to your apps by using Kubernetes Persistent Volumes (PVs).
Click the Catalog button on the top
Select Software from the catalog
Search for IBM Cloud Block Storage plug-in and click on it
On the application page Click in the dot next to the cluster, you wish to use
Click on Enter or Select Namespace and choose the default Namespace or use a custom one (if you get error please wait 30 minutes for the cluster to finalize)
Give a name to this workspace
Click install and wait for the deployment
We will deploy MariaDB on our cluster
Click the Catalog button on the top
Select Software from the catalog
Search for MariaDB and click on it
On the application page Click in the dot next to the cluster, you wish to use
Click on Enter or Select Namespace and choose the default Namespace or use a custom one
Give a unique name to workspace, which you can easily recognize
Select which resource group you want to use, it's for access controll and billing purposes. For more information please visit resource groups
Give tags to your MariaDB Galera, for more information visit tags
Click on Parameters with default values, You can set deployment values or use the default ones
Please set the MariaDB Galera root password in the parameters
After finishing everything, tick the box next to the agreements and click install
The MariaDB Galera workspace will start installing, wait a couple of minutes
Your MariaDB Galera workspace has been successfully deployed
Go to Resources in your browser
Click on Clusters
Click on your Cluster
Now you are at your clusters overview, here Click on Actions and Web terminal from the dropdown menu
Click install - wait couple of minutes
Click on Actions
Click Web terminal, and a terminal will open up
Type in the terminal; please change NAMESPACE to the namespace you choose at the deployment setup:
Enter your pod with bash; please replace PODNAME with your mariadb pod's name
After you are in your pod , please verify that MariaDB is running on your pod's cluster. Please enter the root password after the prompt
You have successfully deployed MariaDB Galera on IBM Cloud!
This page is licensed: CC BY-SA / Gnu FDL
sudo apt-get remove mariadb-server galerasudo yum remove MariaDB-server galerasudo zypper remove MariaDB-server galera$ kubectl get ns$ kubectl get pod -n NAMESPACE -o wide$ kubectl get service -n NAMESPACE$ kubectl exec --stdin --tty PODNAME -n NAMESPACE -- /bin/bashmysql -u root -p -e "SHOW STATUS LIKE 'wsrep_cluster_size'"COMMIT;sudo apt-get remove mariadb-server galerasudo yum remove MariaDB-server galerasudo zypper remove MariaDB-server galera
These topics will be discussed in more detail below.
Dear Schema Designer:
InnoDB only, always have PK.
Dear Developer:
Check for errors, even after COMMIT.
Moderate sized transactions.
Don't make assumptions about AUTO_INCREMENT values.
Handling of "critical reads" is quite different (arguably better).
Read/Write split is not necessary, but is still advised in case the underlying structure changes in the future.
Dear DBA:
Building the machines is quite different. (Not covered here)
ALTERs are handled differently.
TRIGGERs and EVENTs may need checking.
Tricks in replication (eg, BLACKHOLE) may not work.
(This overview is valid even for same-datacenter nodes, but the issues of latency vanish.)
Cross-colo latency is an 'different' than with traditional replication, but not necessarily better or worse with Galera. The latency happens at a very different time for Galera.
In 'traditional' replication, these steps occur:
Client talks to Master. If Client and Master are in different colos, this has a latency hit.
Each SQL to Master is another latency hit, including(?) the COMMIT (unless using autocommit).
Replication to Slave(s) is asynchronous, so this does not impact the client writing to the Master.
Since replication is asynchronous, a Client (same or subsequent) cannot be guaranteed to see that data on the Slave. This is a "critical read". The async Replication delay forces apps to take some evasive action.
In Galera-based replication:
Client talks to any Master -- possibly with cross-colo latency. Or you could arrange to have Galera nodes co-located with clients to avoid this latency.
At COMMIT time (or end of statement, in case of autocommit=1), galera makes one roundtrip to other nodes.
The COMMIT usually succeeds, but could fail if some other node is messing with the same rows. (Galera retries on autocommit failures.)
Failure of the COMMIT is reported to the Client, who should simply replay the SQL statements from the BEGIN.
For an N-statement transaction: In a typical 'traditional' replication setup:
0 or N (N+2?) latency hits, depending on whether the Client is co-located with the Master.
Replication latencies and delays lead to issues with "Critical Reads".
In Galera:
0 latency hits (assuming Client is 'near' some node)
1 latency hit for the COMMIT.
0 (usually) for Critical Read (details below)
Bottom line: Depending on where your Clients are, and whether you clump statements into BEGIN...COMMIT transacitons, Galera may be faster or slower than traditional replication in a WAN topology.
By using wsrep_auto_increment_control = ON, the values of auto_increment_increment and auto_increment_offset will be automatically adjusted as nodes come/go.
If you are building a Galera cluster by starting with one node as a Slave to an existing non-Galera system, and if you have multi-row INSERTs that depend on AUTO_INCREMENTs, the read this Percona blog
Bottom line: There may be gaps in AUTO_INCREMENT values. Consecutive rows, even on one connection, will not have consecutive ids.
Beware of Proxies that try to implement a "read/write split". In some situations, a reference to LAST_INSERT_ID() will be sent to a "Slave".
For effective replication of data, you must use only InnoDB. This eliminates
FULLTEXT index (until 5.6)
SPATIAL index
MyISAM's PK as second column
You can use MyISAM and MEMORY for data that does not need to be replicated.
Also, you should use "START TRANSACTION READONLY" wherever appropriate.
Check for errors after issuing COMMIT. A "deadlock" can occur due to writes on other node(s).
Possible exception (could be useful for legacy code without such checks): Treat the system as single-Master, plus Slaves. By writing only to one node, COMMIT should always succeed(?)
What about autocommit = 1? wsrep_retry_autocommit tells Galera to retry if a single statement that is autocommited N times. So, there is still a chance (very slim) of getting a deadlock on such a statement. The default setting of "1" retry is probably good.
"Row Based Replication" will be used; this requires a PK on every table. A non-replicated table (eg, MyISAM) does not have to have a PK.
(This section assumes you have Galera nodes in multiple colos.) Because of some of the issues discussed, it is wise to group your write statements into moderate sized BEGIN...COMMIT transactions. There is one latency hit per COMMIT or autocommit. So, combining statements will decrease those hits. On the other hand, it is unwise (for other reasons) to make huge transactions, such as inserting/modifying millions of rows in a single transaction.
To deal with failure on COMMIT, design your code so you can redo the SQL statements in the transaction without messing up other data. For example, move "normalization" statements out of the main transaction; there is arguably no compelling reason to roll them back if the main code rolls back.
In any case, doing what is "right" for the business logic overrides other considerations.
Galera's tx_isolation is between Serializable and Repeatable Read. tx_isolation variable is ignored.
Set wsrep_log_conflicts to get errors put in the regular MySQL mysqld.err.
XA transactions cannot be supported. (Galera is already doing a form of XA in order to do its thing.)
Here is a 'simple' (but not 'free') way to assure that a read-after-write, even from a different connection, will see the updated data.
For non-SELECTs, use a different bit set for the first select. (TBD: Would 0xffff always work?) (Before Galera 3.6, it was wsrep_causal_reads = ON.) Doc for wsrep_sync_wait
This setting stalls the SELECT until all current updates have been applied to the node. That is sufficient to guarantee that a previous write will be visible. The time cost is usually zero. However, a large UPDATE could lead to a delay. Because of RBR and parallel application, delays are likely to be less than on traditional replication. Zaitsev's blog
It may be more practical (for a web app) to simply set wsrep_sync_wait right after connecting.
As said above, use InnoDB only. However, here is more info on the MyISAM (and hence FULLTEXT, SPATIAL, etc) issues. MyISAM and MEMORY tables are not replicated.
Having MyISAM not replicated can be a big benefit -- You can "CREATE TEMPORARY TABLE ... ENGINE=MyISAM" and have it existed on only one node. RBR assures that any data transferred from that temp table into a 'real' table can still be replicated.
GRANTs and related operations act on the MyISAM tables in the database mysql. The GRANT statements will(?) be replicated, but the underlying tables will not.
Many DDL changes on Galera can be achieved without downtime, even if they take a long time.
:
Rolling Schema Upgrade (RSU): manually execute the DDL on each node in the cluster. The node will desync while executing the DDL.
Total Order Isolation (TOI): Galera automatically replicates the DDL to each node in the cluster, and it synchronizes each node so that the statement is executed at same time (in the replication sequence) on all nodes.
Caution: Since there is no way to synchronize the clients with the DDL, you must make sure that the clients are happy with either the old or the new schema. Otherwise, you will probably need to take down the entire cluster while simultaneously switching over both the schema and the client code.
Fast DDL operations can usually be executed in TOI mode:
DDL operations that support the NOCOPY and INSTANT algorithms are usually very fast.
DDL operations that support the INPLACE algorithm may be fast or slow, depending on whether the table needs to be rebuilt.
DDL operations that only support the COPY algorithm are usually very slow.
For a list of which operations support which algorithms, see .
If you need to use RSU mode, then do the following separately for each node:
You can 'simulate' Master + Slaves by having clients write only to one node.
No need to check for errors after COMMIT.
Lose the latency benefits.
Remove node from cluster; back it up; put it back in. Syncup is automatic.
Remove node from cluster; use it for testing, etc; put it back in. Syncup is automatic.
Rolling hardware/software upgrade: Remove; upgrade; put back in. Repeat.
- If you are writing to multiple nodes, and you use AUTO_INCREMENT, then auto_increment_increment will automatically be equal the current number of nodes.
/ - Do not use.
- ROW is required for Galera.
- 2
Until recently, FOREIGN KEYs were buggy.
LOAD DATA is auto chunked. That is, it is passed to other nodes piecemeal, not all at once.
DROP USER may not replicate?
A slight difference in ROLLBACK for conflict: InnoDB rolls back smaller transaction; Galera rolls back last.
SET GLOBAL wsrep_debug = 1; leads to a lot of debug info in the error log.
Large UPDATEs / DELETEs should be broken up. This admonition is valid for all databases, but there are additional issues in Galera.
WAN: May need to increase (from the defaults) wsrep_provider_options = evs...
MySQL/Perona 5.6 or MariaDB 10 is recommended when going to Galera.
See .
If all the servers are in the same 'vulnerability zone' -- eg, rack or data center -- Have an odd number (at least 3) of nodes.
When spanning colos, you need 3 (or more) data centers in order to be 'always' up, even during a colo failure. With only 2 data centers, Galera can automatically recover from one colo outage, but not the other. (You pick which.)
If you use 3 or 4 colos, these number of nodes per colo are safe:
3 nodes: 1+1+1 (1 node in each of 3 colos)
4 nodes: 1+1+1+1 (4 nodes won't work in 3 colos)
5 nodes: 2+2+1, 2+1+1+1 (5 nodes spread 'evenly' across the colos)
6 nodes: 2+2+2, 2+2+1+1
Posted 2013; VARIABLES: 2015; Refreshed Feb. 2016
Rick James graciously allowed us to use this article in the documentation.
has other useful tips, how-tos, optimizations, and debugging tips.
Original source:
This page is licensed: CC BY-SA / Gnu FDL
Later, the whole transaction will be applied (with possibility of conflict) on the other nodes.
Critical Read -- details below
- ON: When an IST occurs, want there to be no torn pages? (With FusionIO or other drives that guarantee atomicity, OFF is better.)
- 2 or 0. IST or SST will recover from loss if you have 1.
query_cache_size - 0
query_cache_type - 0: The Query cache cannot be used in a Galera context.
wsrep_auto_increment_control - Normally want ON
wsrep_on - ON
wsrep_provider_options - Various settings may need tuning if you are using a WAN.
wsrep_slave_threads - use for parallel replication
wsrep_sync_wait (previously wsrep_causal_reads) - used transiently to dealing with "critical reads".
SET SESSION wsrep_sync_wait = 1;
SELECT ...
SET SESSION wsrep_sync_wait = 0;SET SESSION wsrep_OSU_method='RSU';
ALTER TABLE tab <alter options here>;
SET SESSION wsrep_OSU_method='TOI';The instructions on this page were used to create the galera package on the Fedora Linux distribution. This package contains the wsrep provider for MariaDB Galera Cluster.
The following table lists each version of the Galera 4 wsrep provider, and it lists which version of MariaDB each one was first released in. If you would like to install Galera 4 using , , or , then the package is called galera-4.
26.4.21
, , , , ,
26.4.20
The following table lists each version of the 3 wsrep provider, and it lists which version of MariaDB each one was first released in. If you would like to install 3 using , , or , then the package is called galera-4.
The following table lists each version of the 2 wsrep provider, and it lists which version of MariaDB each one was first released in.
For convenience, a galera package containing the preferred wsrep provider is included in the MariaDB (the preferred versions are bolded in the table above).
See also .
Install the prerequisites:
Clone from and checkout the mariadb-3.x branch:
Build the packages by executing under thebuild.sh scripts/ directory with the-p switch:
When finished, you will have an RPM package containing the Galera library, arbitrator, and related files in the current directory. Note: The same set of instructions can be applied to other RPM-based platforms to generate the Galera package.
This page is licensed: CC BY-SA / Gnu FDL
25.3.30
, ,
25.3.29
, ,
25.3.28
, ,
25.3.27
,
25.3.26
, ,
25.3.25
, , , ,
25.3.24
, , , , ,
25.3.23
, , , ,
25.3.22
, , , ,
25.3.21
N/A
25.3.20
, , , ,
25.3.19
, , , ,
25.3.18
, , ,
25.3.17
, ,
25.3.16
N/A
25.3.15
, , ,
25.3.14
, ,
25.3.12
25.3.11
N/A
25.3.10
N/A
25.3.9
, ,
25.3.8
N/A
25.3.7
N/A
25.3.6
N/A
25.3.5
, ,
25.3.4
N/A
25.3.3
N/A
25.3.2
,
, , , , , ,
26.4.19
, , , , ,
26.4.18
, , , , , ,
26.4.16
, , , , , , ,
26.4.14
, , , , , ,
26.4.13
, , , , , ,
26.4.12
26.4.11
, , , ,
26.4.9
, ,
26.4.8
, ,
26.4.7
,
26.4.6
,
26.4.5
,
26.4.4
,
26.4.3
,
26.4.2
26.4.1
26.4.0
25.3.37
25.3.35
,
25.3.34
,
25.3.33
,
25.3.32
,
25.3.31
, ,
25.2.9
,
25.2.8
,
23.2.7
sudo yum update
sudo yum -y install boost-devel check-devel glibc-devel openssl-devel sconsgit init repo
cd repo
git clone -b mariadb-3.x https://github.com/MariaDB/galera.gitcd galera
./scripts/build.sh -p